Measure the distance between the vertical balusters on the metal rail with a measuring tape, or refer to the instructions on the railing kit for the spacing between the balusters.
Mark on the concrete stair treads the locations for the brackets that the balusters will fit into, using a marker. Form the marks 2 to 3 inches inward from the edges of the stairs to prevent any cracking when you drill through the concrete. Ensure the marks are spaced evenly along the stairway.
Select a masonry bit that measures a sixteenth-inch smaller than the length of the screws. Position the bit directly above a marked spot on a tread and drill a pilot hole through it. Move up or down the concrete stairway, depending on where you drill the first pilot hole, and continue drilling the remaining holes through the marked spots along the treads.
Hold a bracket over a concrete tread, directly above the pilot hole. Secure the bracket in place using a masonry anchor and a 3-inch screw. Alternatively, secure the bracket using nuts and bolts provided with the railing. Tighten the bolts with a wrench. Repeat this process of setting the brackets in place along the stairway.
Assign a helper to hold one end of the iron railing while you hold the other. Center the lower ends of the balusters directly above the brackets before sliding them through. Use a wrench to tighten the set screws along the ends of the balusters to the brackets.
Attach the top and bottom rails to the vertical balusters according to the manufacturer’s instructions, since these vary. Also attach intermediate rails if they're provided with the railing kit. Secure each piece in place using screws provided with the assembly. Tighten the screws with a screwdriver to anchor them securely to the balusters and prevent the railing from wobbling.